What is this artifact and how to avoid it?
This is the sort of pattern that can arise in the transition between 'kite' quads and more regular quads under subdivision



If you can arrange for the transition to be inside a single-material region rather than at the boundary between materials, it doesn't show:



here, by I insetting the polar region

The Catmull-Clark subdivision algorithm drags newly-created edge-points away from the previous concentrations at one side of a face.. this shows the transition between Simple and Catmull-Clark subdivision: